1. Field of the Invention
The present invention relates to a semiconductor memory device.
2. Description of the Related Art
An electrically writable and erasable nonvolatile semiconductor memory device is formed by stacking a floating gate insulating film, a floating gate electrode, a control gate insulating film and a control gate electrode on a semiconductor substrate (as disclosed in Japanese Patent Application 2006-319202, for example).
In recent years, progress of miniaturization and high integration of semiconductor devices has caused the following problem in a nonvolatile semiconductor memory device such as a NAND flash memory. Specifically, A distance between control gates has been narrowed and accordingly a large capacitance between each adjacent two control gates has been generated. In addition, the width of each control gate electrode used as a word line has been narrowed and accordingly the wiring resistance of the control gate electrode has increased. As a result, a resistance-capacitance (RC) delay component is increased so that the working speed of the memory transistor and other circuit components is decreased.